It is known that foam resins containing urethane groups may be produced by reacting compounds containing active hydrogen atoms with polyisocyanates in the presence of water, catalysts, stabilizers and, optionally, emulsifiers. The catalysts used are preferably tertiary amines.
In most cases, the differing extents to which the catalysts accelerate the reactions of the various components decisively determine the course of the reaction. The formation of a foam is a physico-chemical process in which several inter-connected reactions take place simultaneously. The individual processes result in the formation of the high molecular weight structure (urethane reaction) and in the evolution of carbon dioxide (blowing reaction) and must be finely adjusted. In theory, this may be optimally achieved by using catalysts which specifically catalyze either the urethane reaction or the blowing reaction. By proper catalyst selection, the respective reaction velocities may be proportionally adjusted. Alternately, it may be achieved by means of catalysts which simultaneously and congruently accelerate both reactions so that an optimum foam is obtained from a particular formulation. This means that high quality materials which have uniform properties, and a low specific gravity, (which is frequently desired), may be obtained under ideal operating conditions. The foams should have a faultless pore structure and they should not undergo any shrinkage. Shrinkage has a deleterious effect, particularly in the case of hard foams, which are used for insulating purposes or as supporting materials in composite constructions. Another important criterion is that the product should, as far as possible, be free from odors due to the catalysts.
The catalysts which are technically preferred for accelerating the blowing reaction are bis-(dialkylaminoalkyl)-ethers of the type described in U.S. Pats. Nos. 3,330,782, 2,941,967, and 3,694,510. The catalytic action of these compounds is apparently due to the combined presence of the ether oxygen atom and the tertiary nitrogen atom which are in the .beta.- or .delta. -position to each other.